Synthesis of 2-acetamido-2-deoxy-4-O-(2-O-methyl-beta-D-galactopyranosyl)- D-glucopyranose (N-acetyl-2'-O-methyllactosamine)

Synthesis of 4-nitrophenyl O-(2-acetamido-2-deoxy-beta-D-glucopyranosyl)- (1-->2)-O-(6-O-methyl-alpha-D-mannopyranosyl)-(1-->6)-beta-D- glucopyranoside and its 4',6'-di-O-methyl analog. Potential inhibitors of N-acetylglucosaminyl-transferase V (GnT-V)

O-(2-Acetamido-3,4,6-tri-O-acetyl-2-deoxy-beta-D-glucopyranosyl)-(1-->2) -3,4 - di-O-acetyl-6-O-methyl-alpha-D-mannopyranosyl bromide and O-(2-acetamido-3,4,6-tri-O-acetyl-2-deoxy-beta-D-glucopyranosyl)- (1-->2)-3-O-acetyl-4,6-di-O-methyl-alpha-D-mannopyranosyl bromide were each condensed with 4-nitrophenyl 2,3-di-O-acetyl-beta-D-glucopyranoside, and the products were deprotected to yield, respectively, beta-D-Glc p NAc-(1-->2)-6-O-Me-alpha-D-Man p-(1-->6)-beta-D-Glc p and beta-D-Glc p NAc-(1-->2)-4,6-di-O-Me-alpha-D-Man p-(1-->6)-beta-D-Glc p, as their 4-nitrophenyl glycosides. These trisaccharides are expected to function as inhibitors for N-acetylglucosaminyltransferase V.

Synthesis of benzyl O-(2-O-methyl-beta-D-galactopyranosyl)-(1----3)-2- acetamido-2-deoxy-beta-D-glucopyranoside [benzyl 2'-O-methyllacto-N-bioside I], and its higher saccharide containing an O-(2-O-methyl-beta-D- galactopyranosyl)-(1----3)-2-acetamido-2-deoxy-beta-D-glucopyranosyl group as a potential substrate for (1---4)-alpha-L-fucosyltransferase

Treatment of benzyl O-beta-D-galactopyranosyl-(1----3)-2-acetamido-2- deoxy-4,6-O-isopropylidene-beta-D-glucopyranoside with tert-butylchlorodiphenylsilane afforded the 6'-O-tert-butyldiphenylsilyl ether, which was converted into the 3',4'-O-isopropylidene derivative. Methylation and subsequent removal of protecting groups afforded benzyl O-(2-O-methyl-beta-D-galactopyranosyl)- (1----3)-2-acetamido-2-deoxy-beta-D-glucopyranoside (7). The trisaccharide methyl O-(2-O-methyl-beta-D-galactopyranosyl)-(1----3)-O-(2- acetamido-2-deoxy-beta-D-glucopyranosyl)-(1----3)-beta-D-galactopyranosi de (17) and the tetrasaccharide O-(2-O-methyl-beta-D-galactopyranosyl)-(1----3)-O-(2-acetamido-2-deoxy-b eta-D- glucopyranosyl)-(1----3)-O-beta-D-galactopyranosyl-(1----4)-D-glucopyran ose (32), both containing the 2'-O-methyllacto-N-biose I unit at the nonreducing end, were synthesized, and the structures of 7, 17, and 32 were confirmed by 13C-n.m.r. spectroscopy.

Human splenic galaptin: carbohydrate-binding specificity and characterization of the combining site

A galactose-binding lectin (galaptin) from human spleen has been purified to homogeneity by affinity chromatography on asialofetuin-Sepharose. The carbohydrate-binding specificity of galaptin has been investigated by analyzing the binding of galaptin to asialofetuin in the presence of putative inhibitors. An enzyme-linked immunosorbent assay (ELISA) was developed that involved adsorption of asialofetuin to microtiter plates. Galaptin bound to asialofetuin was detected with polyclonal rabbit anti-galaptin serum followed by goat anti-rabbit IgG-peroxidase conjugate. The concentrations of inhibitors giving 50% inhibition of galaptin binding relative to controls were graphically determined and normalized relative to galactose or lactose. These analyses revealed that galaptin has a combining site at least as large as a disaccharide. The disaccharides having non-reducing-terminal beta-galactosyl residues linked (1,3), (1,4), and (1,6) to Glc or GlcNAc are better inhibitors than free Gal. GalNAc, either free or glycosidically linked, appears to have no affinity for the lectin. The nitrophenyl galactosides are better inhibitors than methyl galactosides, indicating the occurrence of hydrophobic interactions. The data indicate that OH groups at C-4 and C-6 of Gal and the OH at C-3 of GlcNAc in Gal beta(1,4)GlcNAc are important for lectin sugar interaction. Our data support the hypothesis that endogenous receptors for galaptin are most likely lactosaminoglycan moieties.

Serum alpha(1----3)-L-fucosyltransferase, carcinoembryonic antigen, and sialyl Lewis X-i antigen levels in lung cancer

Serum alpha(1----3)-L-fucosyltransferase activity was measured in 58 patients with lung cancer, 27 benign diseases, and in 100 healthy controls. The levels of enzyme activity were significantly higher in the sera of patients with cancer when compared to those in benign diseases and healthy controls. The elevation of the enzyme activity correlated with the clinical stages and to the size of the primary tumors. Follow-up studies with various stages showed that the enzyme activity was useful in tracking the clinical course of disease after surgery. To evaluate the usefulness of this enzyme as a diagnostic marker, carcinoembryonic antigen (CEA) and sialyl Lewis X-i antigen levels were also measured. The results indicate that alpha(1----3)-L-fucosyltransferase could be a more specific tumor marker than such tumor-associated antigens in lung cancer.

Tumor-related elevation of serum (alpha 1----3)-L-fucosyltransferase activity in gastric cancer

(alpha 1----3)-L-Fucosyltransferase activity was measured in serum samples from 90 gastric cancer patients, 10 patients with benign diseases and 100 healthy controls. The enzyme activity was significantly elevated in the serum samples of patients with cancer compared to those from patients with benign diseases (P less than 0.01) and healthy controls (P less than 0.001). The elevation of the enzyme activity was found to correlate strongly with the clinical stage of disease. The sensitivity of (alpha 1----3)-L-fucosyltransferase was also demonstrated to be high in comparison with the tumor-associated antigens, such as carcinoembryonic antigen and sialylated Lewis X-i. Follow-up studies of (alpha 1----3)-L-fucosyltransferase in 11 cancer patients with disease at different stages showed that the enzyme activity could be useful for monitoring the post-surgical course of the disease. These results suggest that (alpha 1----3)-L-fucosyltransferase activity has a clinically important potential as a tumor marker in gastric cancer.

Synthesis of O-alpha-L-fucopyranosyl-(1----3)-O-beta-D-galactopyranosyl-(1----4)-2- acetamido-2-deoxy-D-glucopyranose (N-acetyl-3'-O-alpha-L-fucopyranosyllactosamine)

Methyl 2-O-benzyl-beta-D-galactopyranoside (6) was obtained in five, good yielding steps from methyl beta-D-galactopyranoside (1). Treatment of 1 with tert-butylchlorodiphenylsilane in N,N-dimethylformamide in the presence of imidazole afforded a 6-(tert-butyldiphenylsilyl) ether, which was converted into its 3,4-O-isopropylidene derivative (3). Benzylation of 3 with benzyl bromide-silver oxide in N,N-dimethylformamide, and subsequent cleavage of its acetal and ether groups then afforded 6. On similar benzylation, followed by the same sequence of deprotection, benzyl 2-acetamido-3,6-di-O-benzyl-4-O-[6-O-(tert-butyldiphenylsilyl)-3,4 -O- isopropylidene-beta-D-galactopyranosyl]-2-deoxy-alpha-D-glucopyranoside gave the 2-O-benzyl derivative (10). Compound 10 was converted into its 4,6-O-benzylidene acetal (11). Glycosylation (catalyzed by halide-ion) of 11 with 2,3,4-tri-O-benzyl-alpha-L-fucopyranosyl bromide afforded the fully protected trisaccharide derivative (13). Cleavage of the benzylidene and then the benzyl groups of 13 furnished the title trisaccharide (16). The structure of 16 was established by 13C-n.m.r. spectroscopy.

Synthesis of the isomeric trisaccharides, methyl O-alpha-L-fucopyranosyl- (1----3, 4, and 6)-O-(2-acetamido-2-deoxy-beta-D-glucopyranosyl)-(1----3)-beta- D-galactopyranoside

Benzylation of methyl 3-O-(2-acetamido-4,6-O-benzylidene-2-deoxy-beta-D- glucopyranosyl)-2,4,6-tri-O-benzyl-beta-D-galactopyranoside with benzyl bromide in N,N-dimethylformamide in the presence of sodium hydride afforded methyl 3-O- (2-acetamido-3-O-benzyl-4,6-O-benzylidene-2-deoxy-beta-D-glucopyranosyl) -2,4,6- tri-O-benzyl-beta-D-galactopyranoside (3). Reductive ring-opening of the benzylidene group of 3 gave methyl 3-O-(2-acetamido-3,6-di-O-benzyl-2-deoxy-beta-D- glucopyranosyl)- 2,4,6-tri-O-benzyl-beta-D-galactopyranoside (4). Cleavage of the 4,6-acetal group of 3 with hot, 80% aqueous acetic acid afforded the diol (5). Compounds 3, 4, and 5 were each subjected to halide ion-catalyzed glycosylation with 2,3,4-tri-O-benzyl-alpha-L-fucopyranosyl bromide to produce the corresponding trisaccharide derivatives, which, on catalytic hydrogenation, furnished the title trisaccharides, respectively.